1. Field of the Invention
The present invention relates to encoding systems in which a section of an encoded bitstream is replaced with a new section, and is more particularly related to video encoding systems in which a section of encoded video is replaced in a manner which reduces decoding artifacts.
2. Discussion of the Background
Before compression schemes became available, audio, video, and film could be simply edited by cutting out a section of the audio, video, or film and replacing it with a new or altered section, as desired. However, with the use of compression schemes to encode data, a simple "cut-and-paste" editing procedure may no longer be possible as the information used to construct a frame of video, for example, is at more than one location. Therefore, simply cutting out a section of encoded video may degrade sections of the video which have been unaltered and the new video may contain decoding artifacts if simply inserted into the previously encoded bitstream.
A known solution to this problem in MPEG video encoding is to label a new section of video which is substituted into the old video as being a closed Group Of Pictures (GOP). In MPEG encoding, a closed group of pictures indicates that the predictions used in the B-type frames immediately following the first coded I frame is to use only backward prediction. Alternatively, MPEG allows the use of a flag called "broken_link" which when set indicates that the first B-frames immediately following the first coded I-frame may not be correctly decoded because the reference frame which is used for prediction is not available. The decoder uses this flag to avoid displaying frames that cannot be correctly decoded.
The above solutions will degrade the encoded video and may provide inadequate video quality.